Problem: $ { \left[\begin{array}{rr}{-1} & {0} \\ {1} & {1} \\ {0} & {-1}\end{array}\right]+\left[\begin{array}{rr}{2} & {-1} \\ {-2} & {-2} \\ {4} & {-1}\end{array}\right] = {?} } $
Answer: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rr}{-1}+{2} & {0}+{-1} \\ {1}+{-2} & {1}+{-2} \\ {0}+{4} & {-1}+{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{1} & {-1} \\ {-1} & {-1} \\ {4} & {-2}\end{array}\right]}$